Field of the Invention
This invention relates to a precise position detection device and, more particularly, to such device in which an insensitive zone of an absolute signal consisting of a stepped analog signal formed on the basis of the two-phase incremental position detection signal obtained from an encoder section is eliminated, and an output signal having an approximately linear form may be produced.
Up to now, a variety of different constructions have been employed for this type of the precise position detection devices. The device produced by the present Assignee and shown herein in FIG. 1 may be said to be representative of these known devices, although the title of the literature showing the construction is not recited herein.
Referring to FIG. 1, the numeral 1 designates a rotary encoder having a rotary shaft 1a. When the shaft 1a is rotated in the direction of an arrow mark .theta., a two-phase incremental position detection signals 2, presenting a phase difference of 90.degree. from each other, are transmitted via a jumper wire 3 to an up/down counter 4.
A digital signal 5, corresponding to the amount of the two-phase incremental position detection signal, is supplied from the up/down counter 4 to a D/A converter 6. An analog position signal 7, which is an analog voltage signal in the form of a step wave shown in FIG. 2, is outputted from this D/A converter 6.
The above described conventional precise position detection device has the following disadvantages.
That is, in the above described conventional arrangement, when the rotary shaft la of the encoder section 1 is revolved and the input angle is changed within the "0" value range of the digital value of the analog position signal 7 shown in FIG. 2, the output value of the analog position signal 7 remains to be "0". Thus it is impossible to detect the changes in the input angle .theta. caused by such minute rotation of the rotary shaft 1a.
While the input angle .theta. is changed continuously, the analog position signal 7, detected as a function of the input angle .theta., is in the form of a step wave, as shown in FIG. 2, and thus presents a dead or inoperative zone for the output value of "0". Thus it is impossible to provide a high sensitivity or high precision type position detection device capable of detecting even a minute input angle.
Also, since the analog position signal 7 is in the form of a step signal in its entirety, dead zones are produced not only for the zero digital value, but also for the overall domain including the positive and negative domains, thus lowering the sensitivity and the precision of the detection device.